Tantalum is a shiny, silvery colored metal which is heavy, dense, malleable and ductile when pure. It is found in small quantities in minerals (generally in conjunction with niobium), and is isolated by conversion to the oxide and then the fluoro-complex, K2TaF7, from which the pure metal is obtained by electrolysis. Tantalum is extremely corrosion resistant due to the formation of an oxide film, and is also resistant to acid attack (with the exception of HF). It will react with fused alkalis and a variety of non-metals at elevated temperatures.

Tantalum can be used as a replacement for platinum for laboratory apparatus which has to have good corrosion resistance, and the metal is also used within the chemical industry for similar reasons. The fluids in the human body do not react with the metal and, hence, it is used for surgical implants without rejection. Other applications include the use of tantalum carbide in cemented carbides which are used as cutting tools. The pure metal is used in the electronics industry in the manufacture of various types of electronic equipment (e.g. rectifiers, capacitors, lamp filaments, etc.). Tantalum is also used in vacuum systems as it has a high absorption rate for residual gases. It is also used as an alloying element with, for example, nickel and molybdenum, to produce alloys which have good corrosion resistance, strength and ductility.

Atomic Properties

Atomic number

73

Atomic radius - Goldschmidt ( nm )

0.147

Atomic weight ( amu )

180.9479

Crystal structure

Body centred cubic

Electronic structure

Xe 4f14 5d3 6s2

Ionization potential

No.

eV

1

7.88

2

16.2

Natural isotope distribution

Mass No.

%

180

0.012

181

99.988

Photo-electric work function ( eV )

4.1

Thermal neutron absorption cross-section ( Barns )

22

Valences shown

2, 3, 4, 5

Electrical Properties

Electrical resistivity @20C ( µOhmcm )

13.5

Temperature coefficient @0-100C ( K-1 )

0.0035

Superconductivity critical temperature ( K )

4.47

Thermal emf against Pt (cold 0C - hot 100C) ( mV )

+0.33

Mechanical Properties

Material condition

Soft

Hard

Polycrystalline

Bulk modulus ( GPa )

196.3

Hardness - Vickers

90

200

Poisson's ratio

0.342

Tensile modulus ( GPa )

185.7

Tensile strength ( MPa )

172-207

760

Yield strength ( MPa )

310-380

705

Physical Properties

Boiling point ( C )

5425

Density @20C ( g cm-3 )

16.6

Melting point ( C )

2996

Thermal Properties

Coefficient of thermal expansion @0-100C ( x10-6 K-1 )

6.5

Latent heat of evaporation ( J g-1 )

4165

Latent heat of fusion ( J g-1 )

174

Specific heat @25C ( J K-1 kg-1 )

140

Thermal conductivity @0-100C ( W m-1 K-1 )

57.5

All information and technical data are given as a guide only. Although
every effort has been made to ensure that the information is correct, no
warranty is given as to its completeness or accuracy.